DE3526455C2 - - Google Patents

Description

The invention relates to thermally resistant concrete high strength in the temperature range from 20 ° to 300 ° Celsius for prestressed concrete reactor pressure vessels, in particular for high-temperature nuclear reactors, consisting of one with water-infused mixture of hydraulic cement, Concrete aggregate and additives, optional additives such as Dispersants, retarders, flow agents and fluid loss control agents.

According to DIN 1045, concrete is a building material which is made of cement, concrete aggregate and water and that to influence certain concrete properties concrete additives can also be added. Here causes the mixture of cement and water when hardened Concrete cementing and gluing of the aggregate and thus the establishment of firmness.  It should be noted that both the type and the grain size of the concrete aggregate is essential for the achievable strength of the hardened concrete is.

While concrete usually doesn't have thermal stresses is exposed - you can see from the released Solution heat during the solidification and curing process from -, when using concrete as a building material for prestressed Reactor pressure vessels for nuclear reactors, in particular for High-temperature reactors, from safety-relevant Reason assumed a temperature stress will. Therefore, in these cases, the concrete composition so that the strength properties of the concrete on which the constructive design is based, not inadmissible due to the temperature stress be affected.

Fundamental about the concrete composition is over the 1979 concrete calendar, part 1, known. After that is Concrete aggregate from rock with not too big and itself use as little changing thermal expansion as possible. In addition to the type of rock, the Grain, i.e. the grain size and its distribution, of the concrete aggregate has a great influence on the strength of the concrete. The supplement should be as coarse as possible, however also have little void and not too rich in sand, so that it the lowest possible water or cement paste requirements having.

To the same extent, the concrete should also be as good as possible be processable, that is, the introduction of the concrete in the respective construction should be easy  can. Here, the concrete must be well compacted make sure that there are no cavities that reduce strength can.

These partly conflicting requirements for the surcharge usually lead to mixtures of concrete aggregate different grain sizes, which either by means of standardized sieve lines according to DIN 1045 or above the water demand or with total values for the Grain distribution can be characterized.

In addition to these influencing variables discussed above, which primarily concern the composition of the concrete, are also processing and manufacturing technology as well as economic considerations. With regard to optimal processing of the fresh concrete are generally additives such as flow agents, retarders or dispersant, so as to improve the processing properties of the concrete to the extent required to influence.

Manufacturing aspects concern the sufficient Supply with the necessary components of the concrete, especially with the concrete surcharge as well also the manufacturing security.

One problem that arises during hydration Heat that leads to a rise in temperature Components such as prestressed concrete reactor pressure vessels with thick-walled concrete shell, leads. This caused Under certain circumstances, temperature tensions can crack Result in concrete.

The respective temperature increase and the temperature curve depend essentially on the heat of hydration of the cement, of the cement content of the concrete, of the Fresh concrete temperature, hardening progress and the component dimensions.  

The aim is generally a concrete with a lower Fresh concrete temperature and as low and slower as possible Heat development.

The low fresh concrete temperature can vary Kind be achieved, e.g. B. by using chilled Mixing water, by adding ice cubes to the aggregate or by using liquid nitrogen. The choice of the appropriate starting materials, however, as well the appropriate concrete composition is not just up to align the temperature properties of the concrete also of the required strength and the respective Depending on the conditions of the construction.

Another criterion is heat conduction or the heat storage capacity of the concrete during its Consider service life.

When using concrete in nuclear reactors is also the ability to absorb radioactive radiation from Importance. When building prestressed concrete tanks for reactors of nuclear power plants is next to the radiation resistance of the concrete during the radiation period too its bulk density, the water content of the concrete at high Temperatures and the influence of temperatures on the specific creep of air dry and before drying out protected concrete for single-axis or multi-axis Compressive stress as well as the fatigue strength this concrete with multi-axis pressure load of importance.

The invention is based on this prior art based on the task of a thermally resistant Specify concrete in the temperature range from 20 to  300 ° Celsius has both high strength values that not inadmissible even after a long period of use change, as well as easy to process and is economically producible.

This problem is solved by the characteristics of the characteristic Part of claim 1.

Thereafter, it is intended to choose the composition so that the concrete has a fresh concrete bulk density of more than 2300 kg / m ³ . For this purpose, the proportion of the concrete surcharge is set at a value of 72 to 78% based on the fresh concrete bulk density. The concrete aggregate consists in equal parts of quartz gravel with a grain size of 0 to 8 mm and basalt chippings with a grain size of 8 to 16 mm according to the sieve line Fig. 1. The water cement value, which is the ratio of the water content to the cement content, is set at 0.45. On the one hand, this ensures sufficient workability of the concrete after addition of the plasticizer, and on the other hand the desired strength, in particular pressure resistance, is achieved. Another important feature of the invention relates to the flour grain content, which is set at 27.5 ± 1% of the surcharge. In this context, fly ash is added to the concrete as an additive.

With a target fresh concrete bulk density of 2480 kg / m ³ , the cement portion is 390 kg / m ³ and the portion of fly ash added is 60 kg / m ³ .

According to the invention, it is advantageous blast furnace cement strength class HOZ45L according to DIN 1164. To achieve sufficient processability of the invention  Concrete mix can approx. 1.2% of the concrete Superplasticizers can be added. Processability to extend the fresh concrete, it is advantageous to the concrete mix according to the invention also 0.2% retarder to add.

Sicament 20 has been found to be useful as a flow agent and Plastiment Retarder have been shown to act as retarders.

These and other advantageous embodiments of the invention are specified in the subclaims.

The following are some more achieved with the invention Showing advantages and improvements.  

As already mentioned, prestressed concrete reactor pressure vessels, as are required for nuclear reactors, in particular high-temperature nuclear reactors, are concrete bodies with a large wall thickness. Accordingly, a large volume of fresh concrete, which amounts to several 1000 m ^3, is required for their production. It should also be borne in mind that the required volume of concrete must be made available continuously with the same quality and workability. In particular, the introduction of concrete into components with dense reinforcement requires a relatively high level of compaction effort, since otherwise imperfections in the concrete structure cannot be ruled out. Tailored to such difficult processing conditions, as is normal in a prestressed concrete reactor pressure vessel for nuclear reactors, the composition of the concrete aggregate is determined in such a way that half of the basalt chippings and quartz, so-called gravel sand, are used as the concrete aggregate. It is intended to use the basalt chippings, which, due to the manufacturing process, have an angular and irregular contour of the individual grain, with the larger grain group from 8 to 16 in accordance with the sieve line in FIG. 1, while the grain group 0 to 8 in accordance with the sieve line in FIG. 1 is prescribed for the gravel sand . This requirement serves a dual purpose. On the one hand, the use of basalt, which has higher compressive strength values than quartz according to DIN 52100, promotes the bending tensile strength of the concrete due to the broken shape of the grains, whereby the specified maximum size of 16 allows the workability to be sufficiently good, even with very dense reinforcement; on the other hand, the use of fine-grained quartz means both an improvement in processability and an improvement in the concrete strength at higher temperatures due to the proportion of flour grain (diameter smaller than 0.25 mm) obtained due to the defined sieve line. The reaction of the quartz powder and the fly ash with the calcium hydroxide taking place under hydrothermal conditions results in an increase in strength through the formation of lime silicate.

The flour grain content of about 20% of the fresh concrete bulk density is composed from the cement portion and the two equal portions on added fly ash and the flour of the Quartz surcharge of 60 kg each. On this technically simple Wise, an uneconomical additional need for cement to be avoided as it is due to the binding ability of the Flour grain is compensated for overall.

The concrete composition according to the invention is ideally suited, the requirements for good heat resistance in the temperature range from 20 ° to 300 ° Celsius to meet. But there is also one inexpensive economical manufacture of both Concrete mix as well as the prestressed concrete Reactor pressure vessel for nuclear reactors guaranteed, because due to the mixed grain of the invention Concrete surcharge and the specified weight percentages of cement, concrete aggregate and additives opitmale Processing conditions are observed.

Table 1

Claims (8)

1.Thermally resistant concrete with a fresh concrete bulk density of at least 2300 kg / m ³ with high strength in the temperature interval of 20 ° to 300 ° Celsius for prestressed concrete reactor pressure vessels for nuclear reactors, in particular for high-temperature nuclear reactors, consisting of a water-mixed mixture of hydraulic cement , Concrete aggregate and additives, optional additives such as dispersants, retarders, flow agents, characterized by the following features

• a) the concrete has a fresh concrete bulk density between 2300 and 2800 kg / m ³ ,
• b) the aggregate consists in equal parts of quartz with grain size 0/8 and basalt chippings with grain size 8/16 according to the sieve line Fig. 1 and Tab. 1 and is between 72 and 78% of the fresh concrete bulk density,
• c) fly ash is provided as an additive,
• d) the water cement value is 0.45,
• e) the batch has a flour grain content of 27.5 ± 1% of the surcharge,
• f) Solidification retarders with 0.2% and concrete plasticizers with 1.2% of the fresh concrete bulk density are provided as additives.

2. Thermally resistant concrete according to claim 1, characterized in that the fresh concrete bulk density is 2480 kg / m ³ ± 60 kg / m ³ . 3. Thermally resistant concrete according to one of the preceding claims, characterized in that the content of fly ash is 60 kg per m ³ fresh concrete. 4. Thermally resistant concrete according to one of the previous ones Claims, characterized in that the share in hydraulic cement between 14 and 18% of Fresh concrete bulk density is. 5. Thermally resistant concrete according to one of the previous ones Claims, characterized in that the share in hydraulic cement approx. 16% of the fresh concrete bulk density is. 6. Thermally resistant concrete according to one of the previous ones Claims, characterized in that as hydraulic cement blast furnace cement is provided. 7. Thermally resistant concrete according to one of the previous ones Claims, characterized in that as a hydraulic Cement blast furnace cement of the strength class HOZ45L is provided. 8. Thermally resistant concrete according to one of the preceding claims, characterized in that the proportion of quartz powder (grain size up to 0.25 mm) is 60 kg per m ³ fresh concrete.